remove spurious inclusion of libc.h for LFS64 ABI aliases

the LFS64 macro was not self-documenting and barely saved any
characters. simply use weak_alias directly so that it's clear what's
being done, and doesn't depend on a header to provide a strange macro.

src/linux/fallocate.c

@@ -1,7 +1,6 @@
 #define _GNU_SOURCE
 #include <fcntl.h>
 #include "syscall.h"
-#include "libc.h"
 
 int fallocate(int fd, int mode, off_t base, off_t len)
 {
@@ -10,4 +9,4 @@ int fallocate(int fd, int mode, off_t base, off_t len)
 }
 
 #undef fallocate64
-LFS64(fallocate);
+weak_alias(fallocate, fallocate64);

src/linux/getdents.c

@@ -1,11 +1,10 @@
 #define _BSD_SOURCE
 #include <dirent.h>
 #include "syscall.h"
-#include "libc.h"
 
 int getdents(int fd, struct dirent *buf, size_t len)
 {
 	return syscall(SYS_getdents, fd, buf, len);
 }
 
-LFS64(getdents);
+weak_alias(getdents, getdents64);

src/linux/prlimit.c

@@ -1,7 +1,6 @@
 #define _GNU_SOURCE
 #include <sys/resource.h>
 #include "syscall.h"
-#include "libc.h"
 
 #define FIX(x) do{ if ((x)>=SYSCALL_RLIM_INFINITY) (x)=RLIM_INFINITY; }while(0)
 
@@ -24,4 +23,4 @@ int prlimit(pid_t pid, int resource, const struct rlimit *new_limit, struct rlim
 }
 
 #undef prlimit64
-LFS64(prlimit);
+weak_alias(prlimit, prlimit64);

src/linux/sendfile.c

@@ -1,10 +1,9 @@
 #include <sys/sendfile.h>
 #include "syscall.h"
-#include "libc.h"
 
 ssize_t sendfile(int out_fd, int in_fd, off_t *ofs, size_t count)
 {
 	return syscall(SYS_sendfile, out_fd, in_fd, ofs, count);
 }
 
-LFS64(sendfile);
+weak_alias(sendfile, sendfile64);